You need all of them to make a 6x4 but the cool thing is that they are double sided - one side with a terrain feature and the other side just grass. They also have additional sets (Tundra and Coastal/rivers) and the coastal /river set is very interchangeable with the set I have so you can mix and match tiles. They are also about half the price of many gaming mats that are out there so it's very possible to buy 2 sets for the cost of either 1 FAT Mat or GW mat.